1. Field of the Invention
The present invention relates to a receiver apparatus to which a plurality of receivers can be connected. More particularly, the present invention relates to an LNB (low noise block down converter) with which a satellite broadcast reception system is built.
2. Description of Related Art
FIG. 3 is a block diagram showing an example of a conventional LNB. The LNB 100 shown in this figure includes: a reception circuit 101 that extracts a plurality of channel signals from a satellite signal received via an unillustrated reflector, that then amplifies the extracted signals on a low-noise basis, and that then selects from the amplified signals those requested by receivers 200a and 200b to feed the selected signals thereto; a power supply circuit 102 that generates a supply voltage from which the LNB 100 operates; and ports 103a and 103b to which the receivers 200a and 200b are respectively connected. The power supply circuit 102 includes: diodes Da and Db of which the anodes are respectively connected to the ports 103a and 103b and of which the cathodes are connected together; and regulators REG1 and REG2 whose input terminals are together connected to the cathodes of the diodes Da and Db.
In the LNB 100 configured as described above, the power supply circuit 102 receives, via the ports 103a and 103b, direct-current voltages Va and Vb from the receivers 200a and 200b. The regulators REG 1 and REG2 respectively generate predetermined direct-current voltages VA and VB (for example, 5 [V] and 6 [V]) from the direct-current voltages Va and Vb, and then feed the generated voltages to the relevant parts of the LNB 100.
The direct-current voltages Va and Vb are used not only as the input voltages to the regulators REG1 and REG2, but also as output select signals for the reception circuit 101, each of those signals being shifted among a plurality of voltage levels (for example, between two levels of 13 [V] and 18 [V]) according to the frequency band of the desired channel signal. If the direct-current voltage Va is higher than the direct-current voltage Vb, the diode Da alone is on, and thus the direct-current voltage Va is fed to the regulators REG1 and REG2 as the input voltage thereto; if the direct-current voltage Vb is higher than the direct-current voltage Va, the diode Db alone is on, and thus the direct-current voltage Vb is fed to the regulators REG1 and REG2 as the input voltage thereto.
With the LNB 100 configured as described above, when reception channels are switched, even if there is a difference between the direct-current voltages Va and Vb respectively fed to the ports 103a and 103b, the rectifying action of the diodes Da and Db prevents backflow current from the higher-potential port to the lower-potential port, and thus prevents a receiver breakdown.
However, with the LNB 100 configured as described above, in which the currents Ia and Ib fed from the receivers 200a and 200b, of which a plurality is connected to the LNB 100, are simply added together through diodes for consumption, when there is a difference between the direct-current voltages Va and Vb, all the current consumed by the LNB 100 is extracted solely from the receiver that feeds it with the higher voltage, with no current whatsoever extracted from the other receiver. As a result, with the LNB 100 configured as described above, when reception channels are switched, every time the magnitudes of the direct-current voltages Va and Vb are reversed, the currents Ia and Ib vary greatly, producing noise, and thus resulting in malfunctioning of the LNB 100 and disturbances in received images.
To overcome this problem, in one conventionally disclosed/proposed receiver apparatus, when a plurality of receivers are connected thereto, it extracts current preferentially from the receiver connected to a predetermined port irrespective of the magnitudes of the direct-current voltages fed from the individual receivers (see Japanese Patent Application Laid-Open No. 2002-218329, hereinafter Patent Publication 1). In another conventionally disclosed/proposed receiver apparatus, the total current it consumes is equally distributed among different ports so that equal currents are extracted from a plurality of receivers connected thereto (see Japanese Patent Application Laid-Open No. 2001-127661, hereinafter Patent Publication 2).
Indeed, with the receiver apparatuses disclosed in Patent Publications 1 and 2 mentioned above, when reception channels are switched, even if the magnitudes of the direct-current voltages fed from the a plurality of receivers connected thereto vary, the currents extracted from the individual receivers do not vary. Thus, no noise is produced that results from variations in those currents and that leads to malfunctioning of the receiver apparatus or disturbances in received images.
However, with the receiver apparatus disclosed Patent Publication 1, the current feeding capacity of the receiver connected to a port other than the predetermined one cannot be exploited at all. Thus, when a receiver with a low current feeding capacity is connected to the predetermined port, even if a receiver with a higher current feeding capacity is connected to another port, the receiver apparatus may fail to operate normally because of an insufficient supply of current.
On the other hand, with the receiver apparatus disclosed in Patent Publication 2 (see FIG. 4), the total current it consumes cannot always be distributed equally between the ports 103a and 103b due to variations in the characteristics of the components constituting the distribution circuit DIV (hereinafter referred to as component-to-component variations), producing differences between the values of the currents extracted from the receivers 200a and 200b. Furthermore, the distribution performance of the distribution circuit DIV depends not only on the above-mentioned component-to-component variations but also on variations in the voltages it receives. Thus, even if regulators are provided one for each port in the stage preceding the distribution circuit DIV, slight variations in the voltages the regulators output also produce differences in the values of the currents extracted from the receivers 200a and 200b. Moreover, employing the distribution circuit DIV, the receiver apparatus has a complicated circuit configuration, demanding higher cost and requiring an increased mounting footprint.
In still another conventionally proposed configuration that does not suffer from variations in the currents extracted from a plurality of receivers connected thereto even if the voltages fed from the individual receivers vary, transistor switches and a microcomputer are used to meticulously control how the total current consumed is extracted from each of the plurality of receivers (see Japanese Patent Application Laid-Open No. 2005-102016, Patent Publication 3). With this configuration, however, it takes some time for the transistor switches to perform on/off switching and for the microcomputer to perform signal processing. This makes it difficult to readily follow an instantaneous voltage change (e.g., one resulting form the turning on/off of a receiver). This may cause a failure (e.g., a momentary voltage drop) in the receiver apparatus.